Vladd: OFFICIAL FEEDBACK: 4.2 Celestial Storm on PTS

Does anyone know if it is just rares in the new zone that use IRCs for their drops, or if they have changed existing mobs to use them as well?

Rares are going to use a different system for VP unlike any other zone before. Basically, there will be 2-3 rares up at a time, all the time. You can kill them once a day to get loot and once more at an IRC cost. But, you can only use IRC's once. Every so often, the rares will cycle and there are new targets to kill.